The present invention relates to a seat belt apparatus which is installed on a seat of a vehicle such as an automobile and, in an emergency such as upon collision of vehicles, restrains and protects a passenger (including a driver) by a seat belt. More particularly, the present invention relates to a seat belt apparatus which is installed on a seat having a seat weight measuring unit for measuring the weight of the seat including the weight of the passenger on the seat of the vehicle, and in which a lap anchor to which an end of a lap belt is connected is attached to the vehicle body such as the vehicle floor or the vehicle side wall.
In a vehicle such as an automobile, a seat belt apparatus and an airbag apparatus used simultaneously therewith are provided for the purpose of protecting a passenger sitting down on a seat of the vehicle in an emergency such as upon a collision. The seat belt apparatus protects the passenger, in an emergency, by restraining the passenger at shoulder, chest, and waist. The leading end of the seat belt is connected to the lap anchor. This lap anchor is, in many cases, connected to a lap anchor attached to the vehicle body on the vehicle floor, a vehicle side wall, or a door, considering the layout of the seat belt.
When the seat belt is connected to the vehicle body by the lap anchor as described above, it is possible to prevent the seat belt from disturbing a passenger's sitting down on a vehicle seat or leaving the same. This facilitates getting on and off the vehicle and enables the vehicle to support the belt tension of the seat belt, thereby ensuring more reliable constraint of the passenger. The airbag apparatus protects the passenger by preventing the passenger from colliding with the vehicle body by inertia movement through expansion and deployment of the airbag, in an emergency, used simultaneously with the seat belt apparatus.
There are proposals to further increase the effect of a seat belt apparatus or an airbag apparatus by providing a seat weight measuring unit having load sensors arranged in front and back and to the right and the left of the space under the seat to measure the seat weight including the weight of the passenger sitting on the seat with these sensors and detect the weight of the passenger and the sitting posture of the passenger on the basis of the measured values of the seat weight, and by adjusting the pre-tension of the seat belt in response to the detected passenger weight and the passenger's sitting posture, or adjusting the amount of gas expanded and deployed of the airbag or the expanding and deploying speeds. For example, see Japanese Unexamined Patent Application Publication No. 2001-150997, incorporated by reference herein.
FIG. 3 schematically illustrates a seat belt apparatus 2a installed on a seat having a seat weight measuring unit annexed thereto, as disclosed in Japanese Unexamined Patent Application Publication No. 2001-150997 (incorporated by reference herein). In FIG. 3, reference numeral 1 represents a seat of a vehicle; 1a, a seat cushion on which the passenger sits down; 1b, a seat frame supporting the seat cushion 1a; 1c, a back against which the passenger's back leans upon sitting down on the seat cushion 1a; 2, a seat belt apparatus; 3, seat belt pair out from a retractor R not shown; 4, a lap anchor, attached to the vehicle body, to which the leading end of the seat belt 3 is connected; 5, a tongue slidably supported by the seat belt 3; 6, a buckle attached to the seat frame 1b; 7, a left seat weight measuring unit provided to the left (right in FIG. 3) relative to the passenger at a position between the seat frame 1b and the vehicle floor; and 8, a right seat weight measuring unit provided to the right (left in FIG. 3) relative to the passenger at a position between the seat frame 1b and the vehicle floor.
In such a seat belt apparatus 2a, the seat belt 3 is withdrawn from the retractor after the passenger sits on the seat cushion 1a, to engage the tongue 5 with the buckle 6, thereby causing the passenger to wear the seat belt 3. At this point in time, the weight of the passenger (body weight) is measured by the right and the left seat weight measuring units 7 and 8. In emergency such as upon collision of the vehicle, slack in the seat belt 3 is eliminated by a pretensioner. Simultaneously, a prescribed pre-tension is applied to the seat belt 3, and withdrawal of the seat belt 3 from the retractor is prevented, thereby constraining the passenger by the seat belt 3.
In this case, the upper part of the passenger's body including the shoulder and the chest is contained by the shoulder belt 3a of the seat belt on the retractor side from the tongue 5, and the lower part of the passenger's body including the waist is constrained by the lap belt 3b of the seat belt on the lap anchor 4 side from the tongue 5. Since the pre-strain applied to the seat belt 3 is adjusted in response to the measured passenger's weight, the passenger is more effectively constrained.
When the passenger being conveyed in the automobile is a baby, it is mandatory to use a child seat. In general, the child seat is firmly secured to the seat of the vehicle by the seat belt. When the child seat is thus firmly secured to the seat of the vehicle by the seat belt, a larger belt tension B is applied to the seat belt.
However, since the leading end of the set belt is attached to the vehicle body via the lap anchor, a downward force based on the belt tension B of the seat belt acts on the seat. As a result, the force based on the belt tension B is added to the measured value of the seat weight as measured by the seat weight measuring unit and exerts an influence on the latter. In this case, as disclosed in the above-mentioned Japanese Unexamined Patent Application Publication No. 2001-150997, while the left seat weight measuring unit 7 provided on the buckle 6 side is hardly affected by the force based on the belt tension B, the right seat weight measuring unit 8 on the lap anchor 4 side is easily affected by the belt tension.
Therefore, in the seat weight measuring unit disclosed in Japanese Unexamined Patent Application Publication No. 2001-150997, when securing the child seat, the seat weight is measured by doubling the measured value of the seat weight as measured by the left seat weight measuring unit 7 hardly affected by the force based on the belt tension. This ensures a high reliability of seat weight measurement for the seat weight measuring unit.
For the seat weight measuring unit disclosed in the above-mentioned Japanese Unexamined Patent Application Publication No. 2001-150997, a high reliability of seat weight measurement is ensured by adopting, as the seat weight measured value, a value obtained by doubling the measured value of the left seat weight measuring unit 7 as described above. However, since measured values are different between the right and the left seat weight measuring units 7 and 8, i.e., since the seat weights are imbalanced, the measured values of the left seat weight measuring unit 7 is actually affected considerably by the force based on the belt tension. It is therefore desirable to more reliably measure the seat weight by inhibiting the influence of the force caused by the belt tension as far as possible regarding the measured values of the right and the left seat weight measuring units 7 and 8, by achieving a more balanced state of the seat weight through reduction of the difference between the measured values of the right and the left seat weight measuring units 7 and 8 to the lowest possible level.